Mechanical alloying characteristics and thermal stability of Ti–Al–Si and Ti–Al–Si–C powders

Several stoichiometric ternary Ti–Al–Si and quaternary Ti–Al–Si–C alloys have been prepared by mechanical alloying of elemental powder blends. The structural and morphological evolutions in these powders are characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). XRD results have shown that the elemental powders Ti–Al–Si are progressively transformed into a nanocrystalline solid solution and amorphous phase during mechanical alloying. The results for the powder mixture of quaternary 58Ti–30Al–6Si–6C have shown that supersaturated solid solutions of Ti in nano- and submicro-scales are formed, while Ti5Si3 and TiC compounds are produced in the powder mixture of 50Ti–15Al–20Si–15C. These compositions may be used as distinct precursors for preparing in situ titanium aluminide composites. Investigations on thermal stability of 40 h-milled quaternary powders have indicated that Ti5Si3 is first formed at a lower temperature followed by Al2Ti4C2 and TiC at an intermediate temperature (820 °C). In the case of ternary system a stable Ti5Si3 phase is formed through a series of transitions when heated to 1200 °C. All the above phases are stable at elevated temperatures.